Phase contrast observation



Nov. 3, 1953 M. M. FRANCON PHASE CONTRAST OBSERVATION Filed June 19,1950 Fatenteci Nov. 3,

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UNITED ()FFICE rims :BS

Maurice M. Francon, Paris;=Franc, assignor' .to- Centre National de la'Recherche-Scientifiqii; Paris;-France;a corporation of France It is well-kiiownthat'tfieifietho'dfofobsfer 'tioh by means of phase contrastenableaaii tiga-tion of smalland absolutely trans-p nt' 65-jects,-Which'would be invisible by'coiivemiofiai observation methods.- v

If a" plane waveproducedbj a; {Sin-hole light source located at anihfini distance, is): air 111*- me by means of a comm g deviee'ispropagated through a trafiscarent I-iiedi-ur r'i presenting smallvariationsin thickness or refractive 1 index, said variations iaiis meatchanges in the" phase of the light output andbecome visible through aninstrument if, by of a suitableldevice, said phase variationsareconverted into Iominotis intensity variations;

The above-mentioned result may be'obtained by means of manyknown'devicess In cases of microscopic observation such devices comprisea so-called phase plate, which must belooa'ted on the image of the lightsource produced by the objective. Such a necessity generally impliesserious' 'disadvantage's, amongwhich the follow ing are to be mentioned.

L-Irinearly all present types'of microscope objectives, thefo'cu's islocated within the objective; Transformation of aconventional objec tiveinto a phase contrast-objectivethus necess-i tatesdisarrangin'g andre-arrarlging the objec tive' lenses", which operation is extremely delicate if .all the properties of said vobiective are to be'maintained'.

2; The objective has been-corrected so a's'to provide good qualityimages of an object located contrast mifcsccee," ti itfioiit airydisarrari'e' -l w l I I The'invefitiofi tvill be describedvvith'reffeiice tti'the appended drat'ving' which shows-an ai'cia-lsection of the device. v

half-sphere, for samplers-ace h h intotivop'arts l and"? by a plane 3parallel to the bas'" t me approxi-m tel y located at an equaldistance"fr'irithe ace; 5 ai i eeflterof sa'idsphere: Grifthi-fle ree:the'ha'lf sphere by eschew-reflecting layer a; svi v y r oftitaniumhxide and apiece mace-of an eoaece' central ii-art" or sea 1surrounded by an annular phase pl'a'te 8 is set tlieeefitef Partsiahd'Z' of'the halfso ere aretlie'ir cementedtogether, for example byrfieans of- Caflada; balsam;- or of any similar siibstaiice, arid thesphricaltop-su-rface is made inrthe vicinity of its 'objec't focalplane, but-not of objects located at infinity. Gonsequentlytheim'ag'e'o'f the soureeis generally poor, it bears numerous aberrationsand the phase plate cannot s'creeri' its totalit Light rays'dirira'cfiea by the transparent-object-are thusmixed with direct raysdue to aberrations. Such effects are eveifin'creaseci by flaws irr'thecondenser used as" a collimator;

3. Fina1ly,vthe'- direct-wave} While being propagated through theobjective, produces animportant parasite light, d'ueboth to aberrationsand parasite reflections. V i

Oneobject of" the present invention is to pro vide a device locatedexternally of the microscope I and givinganimage in phase contrast whichmay be-directly observed.-

Another object of the present-invention is to prov-idea device whichenables-immediate-conversion of a conventional:mioroscopeiinto-a phaserefieeti-vefor instance by means of'an aluminium deposit, except foraismall areasurrounciing" the agree 5; arid -theiclimensionsnofgwhiclrare' sub-- st'antia'lly the same as those of the opaque'por ti'onor'spotz'l-ofthe phase plate;

Phase plate 8/ maybeembedded in either of parts l or! ofthehalf-spherasuitably cut away for such purpose, or ,Ganada balsamerany similar substance capable of cementing the halfsphere partstogether,

Thedevice then operates'as follows, 7 v

The objectto be investigated is placed in the vicinity of the center fi'of the half sphre, It receives a; ligl' t beam from a light source, animage of which is formedon the surface consisting of the central opaquezone land the phase plate 8' by meanspf a condenser. Neith ef'the' saidsource nor the said condensrareshooifi ifi" the wie Directions of; thelight rays are as follows:

Di-rect light-:The portion of direct" light falling ontofihe ce alopaqfie are l of the phase plate is partially -rejfiect ed; ownwards;but it does notpass throughtrari 'farefft acres; and", consequently itpe etiat into t ob" jective a of the microscope. A direct light rayhaving passed; through the annular' phase plate 8 is reflected by thecurved refiectin g surfaoe, and is again; partially reflected onthesemi-refiecting surface and emerges at 5' to enter the microscopeobjective.

fim t-+ 11 considering now alight ray H} d-ifi'ractedbythe transparentobject located at- 6, it--may be seenthat part ofsuch ray ispropagatemwithout deviation, through the 1 semi refiectinglayer,reaching at 12'therefiect- 3 ing portion of the sphere, is reflected back thereby, isthen partially reflected by the semi-reflecting layer, emerges from thehalf-sphere at 5, and then enters objective 9. Part of the ray isreflected as indicated by the broken line arrow, and is effectivelylost.

All light rays from a determined point of the object situated nearcenter 6 thus exactly pass through one same point near apex 5.

The device thus performs a strictly anastigmatic and aplanitictransmission of the image of an object and enables to set the phaseplate in position in front of the optical observation system. The imageresulting from said transmission is a directly observable phasecontrasted image.

Particularly such an image may be observed through a lens or aconventional microscope without any previous transformation. Shiftingfrom normal observation to phase contrast observation is thus an easyoperation.

It is only necessary to insert the above-described device between thecondenser and the objective of the microscope, the specimen being placedat 6.

This device may be adapted as well to dry objectives as to immersionobjectives and makes it possible to use numerical openings up to 1.35.

What I claim is:

1. An optical phase contrast observation device comprising a firstportion of a sphere of transparent material limited by two parallelplanes one of which is a diametral plane of said sphere, the other planebeing at a distance from the first plane substantially equal to one halfof the radius of said sphere, a second portion of a sphere oftransparent material similar to that of said first portion, completingsaid first portion to form a hemisphere, said two sphere portions beingassembled to form a hemisphere with a base and a separating surfaceparallel to said base, a layer of half-transparent, half-reflectingmaterial being inserted between the two sphere portions over the wholeof said separating surface, a plane, circular phase plate adapted toproduce a difference of phase between light rays passing through it andlight rays passing outside said plate, said plate having a centralcircular opaque spot disposed centrally of said separating surface, theexternal surface of said second sphere portion being covered by a layerof reflecting material, except for a spot at the apex of the hemisphere,said last named spot having substantially the same measurements as saidopaque spot.

2. An optical phase contrast observation device comprising a firstportion of a sphere of transparent material limited by two parallelplanes one of which is a diametral plane of said sphere, the other planebeing at a distance from the first plane substantially equal to one halfof the radius of said Sphere, a second portion of a sphere oftransparent material similar to that of the first portion, completingsaid first portion to form a hemisphere, said hemisphere having a baseand a separating surface parallel to said base, the surface of one ofsaid portions corresponding to said separating surface being covered bya layer of a half-transparent, half-reflecting material, a circularrecess being provided in the central part of the surface of one of saidportions corresponding to said separating surface, a plane, circularphase plate adapted to produce a difference of phase between rays oflight passing through it and rays of light passing outside it, saidphase plate having an opaque central circular spot and said plate beingarranged in said recess, parallel to said separating surface, theexternal surface of said second sphere portion being covered by a layerof reflecting material, except for a spot at the apex of the hemisphere,said last named spot having substantially the same measurements as saidopaque spot.

3. An optical phase contrast observation device comprising a firstportion of a sphere of transparent material limited by two parallelplanes one of which is a diametral plane of said sphere, the other planebeing at a distance from the first plane substantially equal to one halfof the radius of said sphere, a second portion of a sphere oftransparent material similar to that of said first portion, completingsaid first portion to form a hemisphere, said two sphere portions beingcemented together by means of a substance providing substantially thesame refractive index as the two sphere portions, to form a hemispherehaving a base and a separating surface parallel to said base, thesurface of one of said portions corresponding to separating surfacebeing covered by a layer of a half-transparent, half-reflectingmaterial, a plane, circular phase plate having an opaque centralcircular spot being embedded at the central part of said separatingsurface, Within the material by means of which the two sphere portionsare united, and the external surface of said second sphere portion beingcovered by a layer of reflecting material, except for a spot at the apexof the hemisphere, said last named spot having substantially the samemeasurements as said opaque spot.

t. An optical phase contrast observation device comprising a firstportion of a sphere of transparent material limited by two parallellanes one of which is a diametral plane of said sphere, the other planebeing at a distance from the first plane substantially equal to half theradius of said sphere, a second sphere portion of transparent materialsimilar to that of first portion, completing said first portion to forma hemisphere, said two sphere portions being assembled to form ahemisphere with a base and a separating surface parallel to said base, alayer of halftransparent, half-reflecting material between the twosphere portions over the whole of said separating surface, an opaque,circular spot disposed centrally on said separating surface, and aplane, annular phase plate disposed immediately around said central spoton said separating surface, the external surface of said second sphereportion being covered by a layer of reflecting material, except for aspot at the apex of the hemisphere, said last named spot havingsubstantially the same measurements as said opaque spot.

MAURICE M. FRANOON.

References Cited in the file of this patent UNITED STATES PATENTS NameDate Kaprelian June 12, 1945 OTHER REFERENCES Number "was-Iii

